There will still be roads. They are needed for pedestrians and bicyclists. But they are not commonly open for car traffic. Here in Munich, there are large pure pedestrian zones. But some of them a free for bicyclists after 9pm in the evening and in the morning hours (like 8-10) delivery traffic is allowed. And the police and ambulance cars can drive it any time it is needed.
Well, the roads still could be built to support the load of an occasional heavy truck, whatever the traffic limitations on that road are. And in most places, there are existing roads which carry the necessary loads. The repurposing would at most affect the topmost layer.
